Optical pickup device, recording and reproducing apparatus and gap detection method

ABSTRACT

An optical pickup device and an optical recording and reproducing apparatus are suitable for use with a near-field optical recording and reproducing system. An optical pickup device comprises an objective lens composed of a solid immersion lens (SIL) the objective lens having a numerical aperture greater than 1, a beam splitter configured to reflect both of a p-polarized light component and an s-polarized light component of reflected lights from an optical recording medium when the optical pickup device irradiates the optical recording medium with a bundle of rays in a predetermined polarized state from a light source through the objective lens, a divider configured to divide incident light into a p-polarized light component and an s-polarized light component reflected by the beam splitter, and a photo-detector configured to separately detect the p-polarized light component and the s-polarized light component divided by the divider.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/714,866, filed Nov. 18, 2003, and is based upon and claims thebenefit of priority from prior Japanese Patent Application No.2002-341378, filed Nov. 25, 2002, the entire contents of each of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup device, and anoptical recording and reproducing apparatus including this opticalpickup device (this optical recording and reproducing apparatus containsa magneto-optical recording and reproducing apparatus) and a gapdetection method, and more particularly to an optical pickup device, anoptical recording and reproducing apparatus and a gap detection methodfor use with a so-called near-field optical recording and reproducingsystem for recording and/or reproducing an optical recording mediumwhile an optical lens is increasing its numerical aperture.

2. Description of the Related Art

Optical recording mediums, which are typically available in the form ofa compact disc (CD), a mini disc (MD) and a digital video disc (DVD),have been so far widely used as storage mediums for storing thereinmusic information, video information, data, programs and the like(“optical recording medium” in this specification refers to not only theoptical recording medium but also a “magneto-optical recording medium”).

These optical recording mediums can be recorded and/or reproduced bylaser beams irradiated on the signal recording surface of the opticalrecording medium from the optical pickup device. Specifically, when theoptical recording medium is reproduced by an optical pickup deviceaccording to the related art, for example, very small changes ofreflectance are read out from pits formed on one side of the opticalrecording medium through a non-contact objective lens, which is not incontact with the optical recording medium, such as an objective lens ofa microscope. In the magneto-optical detection, miniscule magneticdomains are read out from the magneto-optical disk based upon a Kerrrotation angle.

The diameter of beam spot on the optical disk is roughly given by λ/NA(where λ represents the wavelength of illumination light and NArepresents the numerical aperture of the lens), and resolution isproportional to the value given by this equation. With respect to thenumerical aperture NA, the following equation is established:NA=n·sin θ(where n represents the refractive index of the medium and θ representsthe angle of rays of light around the objective lens).

When the medium is air, the numerical aperture NA is inhibited fromexceeding 1. As a technology that can surpass this limit, there has beenproposed an optical pickup device of a near-field optical recording andreproducing system using “solid immersion lens (see the followingnon-patent document 1).

The solid immersion lens (SIL) has the same refractive index as that ofan optical disk substrate, and is shaped like a part of a sphereincluding a spherical surface portion and a flat surface portion, theflat surface portion thereof being very close to the surface of theoptical recording medium. Evanescent wave transmits through the boundarysurface between the solid immersion lens and the optical disk, and thisevanescent wave reaches the signal recording surface of the opticaldisk.

Non-Patent Document 1:

I. Ichimura et. al, “Near-Field Phase-Change Optical Recording of 1.36Numerical Aperture.” Jpn. J. Appl. Phys. Vol. 39, 962-967 (2000)

Since it is customary for the above-mentioned optical pickup device toread an information signal from the optical disk while the optical diskis being rotated, the optical disc and the solid immersion lens have torequire a gap (space) therebetween. Therefore, the evanescent waveshould be used in order to achieve the numerical aperture NA greaterthan 1. Since the evanescent wave attenuates exponentially from theinterface, the gap between the optical disk and the solid immersion lensshould be made extremely thin, i.e., approximately 10/1 of thewavelength λ of light from the light source of the optical pickupdevice, for example. Moreover, in order to reduce the area of the gap,the gap has to approach the signal recording surface of the opticaldisk.

As a method for controlling the above gap, there has hitherto beenproposed a method for servo-controlling a distance (gap) between a solidimmersion lens and an optical disk based upon a gap error signal afterthe gap error signal has been obtained by detecting an electrostaticcapacity between an electrode formed on the surface of the solidimmersion lens and the optical disk.

However, in order to execute this previously-proposed method, theelectrode has to be formed on the surface of the solid immersion lensand a signal line has to be led from this electrode to a control circuitso that the optical pickup device becomes complex in arrangement, andhence it becomes difficult to manufacture the optical pickup device.

On the other hand, in the mastering process of the optical disk, theassignee of the present application has previously proposed a method forusing returned light detected from a glass master disk as a gap errorsignal (see Japanese patent application No. 10-249880).

When the solid immersion lens and the glass master disk have no gaptherebetween, the surface of the solid immersion lens is in contact withthe transparent photoresist on the glass master disk, and hence no lightis returned from the surface of the solid immersion lens. Conversely,when the solid immersion lens and the glass master disk have the gaptherebetween, light that has been totally reflected on the surface ofthe solid immersion lens is returned. The above previously-proposedmethod is able to detect the gap between the solid immersion lens andthe glass master disk by using this returned light.

However, this previously-proposed method can be used only when themaster disk is made of glass and the photoresist for use in exposure istransparent. If the master disk has a reflective film such as analuminum film, a phase-change film and a magneto-optical recording filmdeposited on its surface like an optical disk, then even when the solidimmersion lens and the master disk have no gap therebetween, light isreflected on the surface of the optical disk and no light is returned.Hence, this previously-proposed method cannot be used.

In order to solve the above-mentioned problem, the assignee of thepresent application has previously proposed an optical pickup devicethat can accurately detect a very small gap between an optical disk witha reflective film deposited on its surface and a solid immersion lens(see Japanese patent application No. 2001-264467).

The above previously-proposed optical pickup device will be describedbelow with reference to the drawings.

FIG. 1 of the accompanying drawings is a side view showing anarrangement of an example of this optical pickup device.

As shown in FIG. 1, the optical pickup device includes an objective lens2 composed of a solid immersion lens (SIL) 1 having a spherical portionand a flat surface portion parallel to the surface of an opticalrecording medium 90 to form a part of a shape of a sphere, the objectivelens 2 having a numerical aperture greater than 1. The solid immersionlens 1 is shaped like a hemisphere, for example, and has a thicknesssubstantially equal to the radius of the sphere. A distance (gap)between the flat surface portion of the solid immersion lens 1 and thesurface of the optical recording medium 90 can be held at approximately10/1 of the wavelength of light emitted from a semiconductor laser 3serving as a light source under control of a servo mechanism which willbe described later on.

This optical pickup device is able to obtain a gap error signalcorresponding to a distance between the surface of the optical recordingmedium 90 and the flat surface portion of the solid immersion lens 1 bydetecting a component of the polarized state perpendicular to thepolarized state of reflected light obtained when the surface of theoptical recording medium 90 and the flat surface portion of the solidimmersion lens 1 have no gap therebetween from reflected lights(returned lights) reflected on the optical recording medium 90 afterthey have been emitted from the semiconductor laser 3.

Specifically, in this optical pickup device, a bundle of rays emittedfrom the semiconductor laser 3 is collimated by a collimator lens 4 as abundle of parallel rays and introduced into a beam splitter 5. A bundleof rays emitted from the semiconductor laser 3 has a wavelength of 400nm, for example. A bundle of rays emitted from the semiconductor laser 3transmits through the beam splitter 5 and becomes incident on apolarization beam splitter 6. A bundle of rays emitted from thesemiconductor laser 3 is a p-polarized light relative to the reflectionsurface of the polarization beam splitter 6, and hence it transmitsthrough the reflection surface of the polarization beam splitter 6,whereafter it transmits through the polarization beam splitter 6.

A bundle of rays that has transmitted through the polarization beamsplitter 6 transmits through a λ/4 plate (quarter-wave plate) 7 with itscrystallographic axis inclined at an inclination angle of 45° relativeto the direction of the incident polarized light, by which it isdouble-refracted so as to become circularly polarized light and thecircularly polarized light is introduced into an objective lens 8comprising the condenser lens 2 together with the solid immersion lens1. A bundle of incident parallel rays is converged by this objectivelens 8 and introduced into the solid immersion lens 1. This solidimmersion lens 1 has a focal point formed near a parallel portiondisposed parallelly close to the surface of the optical recording medium90. A refractive index of the solid immersion lens 1 is selected to be1.8, for example.

A bundle of the thus converged rays is converged on the signal recordingsurface of the optical recording medium 90 as evanescent wave. In thiscase, the objective lens 2 has an NA (numerical aperture) ofapproximately 1.36, for example.

The optical pickup device shown in FIG. 1 is constructed as the opticalpickup device capable of reproducing either an optical disk on which aninformation signal is recorded by recording pits (concavities andconvexities) or a recordable optical disk on which an information signalis recorded by using phase-change. Specifically, a bundle of rays thathas been converged on the signal recording surface of the opticalrecording medium 90 is reflected in various manners with or withoutapplication of the recording pits on this signal recording surface andreturned to the polarization beam splitter 6 through the objective lens2 and the quarter-wave plate 7.

A bundle of rays returned to the side of the condenser lens 3 after ithas been reflected on the surface of the optical recording medium 90 isintroduced into the quarter-wave plate 7, in which it isdouble-refracted in the form of circularly polarized light to linearlypolarized light. At that time, the direction of polarized light isnormal to the direction of polarization of a bundle of rays emitted fromthe semiconductor laser 3. Accordingly, a bundle of rays returned afterit has been reflected on the surface of the optical recording medium 90is s-polarized light relative to the reflection surface of thepolarization beam splitter 6 and thereby reflected on the reflectionsurface of the polarization beam splitter 6 so that it is deviated fromthe light path along which it may return to the semiconductor laser 3,thereby being received at a first photo-detector 9 which is used toobtain a reproduced signal from the optical recording medium 90.

According to this optical pickup device, on the surface A between thebeam splitter 5 and the polarization beam splitter 6, a bundle of raysemitted from the semiconductor laser 3 is linearly polarized lightcontaining only an electric field component of X direction as shown inFIG. 2A but which does not contain an electric field component of Ydirection as shown in FIG. 2B.

Then, in the state in which the flat surface portion of the solidimmersion lens 1 is in close contact with the surface of the opticalrecording medium 90, this flat surface portion is in close contact witha phase-change recording and reproducing multilayer film (composed of Alfilm, SiO₂ film, GeSbTe film, SiO₂ film deposited on the substrate, inthat order) deposited on the surface of the optical recording medium 90as shown in FIG. 3A or a reflective film made of a suitable materialsuch as aluminum (Al film deposited on a substrate) deposited on thesurface of the optical recording medium 90 as shown in FIG. 3B.

As described above, in the state in which the flat surface portion ofthe solid immersion lens 1 is in close contact with the surface of theoptical recording medium 90, most of reflected light is inwardly andoutwardly transmitted through the quarter-wave plate 7 and thereby thereflected light is double-refracted so as to have the direction ofpolarization rotated 90° so that a bundle of rays with a distributionsubstantially equal to that of light emitted from the semiconductorlaser 3 may become incident on the surface B that is the surface justahead of the first photo-detector 9 as shown in FIG. 4A. At that time,as shown in FIG. 4B, reflected light is hardly returned from the opticalrecording medium 90 to the surface A between the beam splitter 5 and thepolarization beam splitter 6.

Then, in the state in which the solid immersion lens 1 is away from theoptical recording medium 90, as shown in FIG. 5, of light beamsconverged near the flat surface portion of the solid immersion lens 1, alight beam that will become incident on the flat surface portion at anincidence angle greater than a critical angle in this flat surfaceportion is reflected on the flat surface portion ((refractive index ofsolid immersion lens)×sin (incidence angle)>1).

In the thus reflected light, its direction of polarization is rotateddelicately when it is totally reflected. The light beam that has beentotally reflected as described above contains a polarized lightcomponent perpendicular to the reflected light obtained in the state inwhich the flat surface portion of the solid immersion lens 1 is in closecontact with the surface of the optical recording medium 90 as describedabove. As a result, a distribution of the returned light on the surfaceA between the beam splitter 5 and the polarization beam splitter 6becomes a distribution in which only light beams at the portionscorresponding to the marginal portions of a bundle of rays are returnedas shown in FIG. 6A.

The light beam that has returned to the surface A as described above isreflected on the reflection surface of the beam splitter 5 and receivedat a second photo-detector 10 which is used to obtain a gap error signalas shown in FIG. 1. This gap error signal is a signal corresponding to adistance between the flat surface portion of the solid immersion lens 1and the optical recording medium 90.

Then, at that time, a distribution of the returned light beam on thesurface B located just ahead of the first photo-detector 9 becomes adistribution in which returned light beams at the portions correspondingto the marginal portions of a bundle of rays are missed.

In a relationship between a quantity of light received at the secondphoto-detector 10 and the distance (air gap) between the flat surfaceportion of the solid immersion lens 1 and the surface of the opticalrecording medium 90, this distance (air gap) can be held at 10/1 of thewavelength by controlling the position at which the solid immersion lens1 comes in contact with or comes away from the optical recording medium90 in such a manner that the quantity of light at the secondphoto-detector 10, for example, may be kept at the ratio of quantity ofincident light of 0.2 as shown in FIG. 7.

When the optical recording medium 90 is a magneto-optical disk, anoptical pickup device having an arrangement shown in FIG. 8, forexample, can be applied to this example. Specifically, as shown in FIG.8, a bundle of rays emitted from the semiconductor laser 3 is convergedon the signal recording surface of the optical recording medium 90through the collimator lens 4, the polarization beam splitter 6, thebeam splitter 5, the condenser lens 8 and the solid immersion lens 1. Inthis optical pickup device, a quarter-wave plate is not provided on theoutward light path to the optical recording medium 90.

Then, the returned light beam that has been reflected on the opticalrecording medium 90 is divided by the beam splitter 5, whereafter it isrefracted by a λ/2 plate (half-wave plate) 11 (i.e., polarizationfilter) so that its direction of polarization is rotated 45° andintroduced into a second polarization beam splitter 12. This half-waveplate 11 is disposed with its optical axis inclined 22.5° relative tothe direction of incident linearly polarized light.

The light beam that became incident on the second polarization beamsplitter 12 is divided in response to a Kerr rotation angle generatedbased on a magneto-optical effect when it is reflected on the signalrecording surface of the optical recording medium 90, and it is receivedat the first and second photo-detectors 13 and 14, both of which areused to obtain a magneto-optical signal. A difference signal betweenoutputted signals from the first and second photo-detectors 13, 14 isnot generated when a bundle of reflected rays does not generate the Kerrrotation angle and becomes an output corresponding to the Kerr rotationangle generated in a bundle of reflected rays, which becomes amagneto-optical signal.

Then, a bundle of rays that has returned from the flat surface portionof the solid immersion lens 1 in order to obtain the gap error signal isreturned through the beam splitter 5 to the polarization beam splitter6. Then, it is reflected by this polarization beam splitter 6 andreceived at the third photo-detector 10 that is used to obtain the gaperror signal.

When the optical recording medium 90 is the magneto-optical disk, theoptical pickup device may be modified as an optical pickup device havingan arrangement shown in FIG. 9, for example. Specifically, as shown inFIG. 9, a bundle of rays emitted from the semiconductor laser 3 may beconverged on the signal recording surface of the optical recordingmedium 90 through the collimator lens 4, the beam splitter 5, thecondenser lens 8 and the solid immersion lens 1.

The light beam that has been irradiated on the signal recording surfaceof the optical recording medium 90 in this manner is reflected on thissignal recording surface and reflected on the beam splitter 5,whereafter it is further divided by the second beam splitter 15 into twobundles of rays. A bundle of rays that has passed the second beamsplitter 15 is transmitted through the half-wave plate 11 and therebyits direction of polarization is rotated 45°, whereafter it isintroduced into the polarization beam splitter 12. This half-wave plate11 is located such that its optical axis is inclined at an inclinationangle of 22.50 relative to the direction of incident linearly polarizedlight.

The light beam that has been introduced into the polarization beamsplitter 12 is divided in response to the Kerr rotation angle generatedby the magneto-optical effect when it is reflected on the signalrecording surface of the optical recording medium 90 and received at thefirst and second photo-detectors 13 and 14 which are used to obtain themagneto-optical signal. A difference signal between the outputtedsignals from the first and second photo-detectors 13, 14 is notgenerated when a bundle of reflected rays does not have the Kerrrotation angle, and becomes an output corresponding to the Kerr rotationangle generated in this bundle of rays, which becomes a magneto-opticalsignal.

On the other hand, a bundle of rays reflected by the second beamsplitter 15 is introduced into the second polarization beam splitter 16.Of this bundle of rays, a bundle of rays that has returned from the flatsurface portion of the solid immersion lens 1 in order to obtain the gaperror signal is reflected by the second polarization beam splitter 16and received at the third photo-detector 10 that is used to obtain thegap error signal.

Also in the optical pickup device shown in FIG. 9, similarly to the caseof the optical system shown in FIG. 1, the polarized state of incidentlight introduced into the beam splitter 5 becomes linearly polarizedlight that contains only the electric field component of the X directionas shown in FIG. 2A but that does not contain the electric fieldcomponent of the Y direction as shown in FIG. 2B. Each of the beamsplitters 5, 15 transmits and reflects the polarized components of bothX, Y directions equally.

When the flat surface portion of the solid immersion lens 1 is in closecontact with the surface of the optical recording medium 90, this flatsurface portion is in close contact with the phase-change recording andreproducing multilayer film (composed of Al film, SiO₂ film, TeFeCofilm, SiO₂ film deposited on the substrate, in that order) deposited onthe surface of the optical recording medium 90 as shown in FIG. 10. Adistribution of returned light on the surface B which is the surfacerequired after the returned light has passed through the secondpolarization beam splitter 16 at that time becomes a distributionsubstantially equal to those of light beams emitted from thesemiconductor laser 3 as shown in FIG. 11A. Then, in the surface C whichis the surface disposed just before returned light is reflected by thesecond polarization beam splitter 16 and introduced into the thirdphoto-detector 10, the returned light from the optical recording medium90 is hardly returned as shown in FIG. 11B. Accordingly, when the flatsurface portion of the solid immersion lens 1 is in close contact withthe surface of the optical recording medium 90, returned light on thesurface C is almost zero, and hence returned light hardly reaches thethird photo-detector 10.

Then, in the state in which the solid immersion lens 1 is distant fromthe optical recording medium 90, as shown in FIG. 5, of light beamsconverged near the flat surface portion of the solid immersion lens 1,light incident on the flat surface portion of the solid immersion lens 1at an angle exceeding the critical angle of this flat surface portion istotally reflected on this flat surface portion of the solid immersionlens 1 ((refractive index of solid immersion lens)×sin(incidenceangle)>1)

The thus totally reflected light delicately rotates its direction ofpolarization when it is totally reflected. Then, the thus totallyreflected light contains a polarized component normal to the reflectedlight obtained in the state in which the flat surface portion of thesolid immersion lens 1 is in close contact with the surface of theoptical recording medium 90 as described above. As a result, adistribution of the returned light on the surface C which is the surfacerequired just before the light is reflected by the second polarizationbeam splitter 16 and introduced into the third photo-detector 10 becomesa distribution in which the portions corresponding to the marginalportions of a bundle of rays are partly returned as shown in FIG. 12B.

The light thus returned to the surface C is received at the secondphoto-detector 10 which is used to obtain a gap error signal. This gaperror signal is a signal corresponding to the distance between the flatsurface portion of the solid immersion lens 1 and the surface of theoptical recording medium 90.

Then, at that time, a distribution of the returned light on the surfaceB which is the surface behind the second polarization beam splitter 16becomes a distribution in which the portions corresponding to themarginal portions of a bundle of rays are missing as shown in FIG. 12A.

In a relationship between the quantity of light received at the thirdphoto-detector 10 and the distance (air gap) between the flat surfaceportion of the solid immersion lens 1 and the surface of the opticalrecording medium 90, as shown in FIG. 13, this distance (air gap) can beheld at 10/1 of the wavelength of the light by controlling the positionof the direction in which the solid immersion lens 1 comes in contactwith or comes away from the optical recording medium 90 such that thequantity of light of the third photo-detector 10, for example, is heldat the ratio of quantity of incident light of 0.1.

However, when these previously-proposed optical pickup devices are inuse, the arrangement shown in FIG. 1 requires a plurality of beamsplitters such as the beam splitter 5 for obtaining the gap error signaland the polarization beam splitter 6 for obtaining the reproduced signaland also requires separately independent photo-detectors such as thephoto-detector 10 for obtaining the gap error signal and thephoto-detector 9 for obtaining the reproduced signal. There arises aproblem, in which the optical pickup device becomes complex inarrangement. The optical pickup devices shown in FIGS. 8 and 9 needsmuch more beam splitters and photo-detectors. Further, a problem arises,in which the recording and reproducing apparatus requires the opticalpickup device having the complex arrangement so that the recording andreproducing apparatus which assembles such optical pickup device alsobecomes complex in arrangement.

SUMMARY OF THE INVENTION

In view of the aforesaid aspects, it is an object of the presentinvention to provide an optical pickup device, a recording andreproducing apparatus and a gap detection method in which a distancebetween a recording medium and a solid immersion lens can be detectedand controlled with ease in this kind of near-field optical recordingand reproducing system.

According to an aspect of the present invention, there is provided anoptical pickup device including a condenser lens composed of a solidimmersion lens having a spherical surface portion and a flat surfaceportion parallel to the surface of an optical recording medium, thecondenser lens having a numerical aperture greater than 1, a bundle ofrays in a predetermined polarized state being irradiated on the opticalrecording medium from a light source through the condenser lens and apolarized state component perpendicular to the polarized state ofreflected light obtained when a distance between the surface of thisoptical recording medium and the flat surface portion of the solidimmersion lens is zero is detected from reflected light from the opticalrecording medium to obtain a signal corresponding to the distancebetween the surface of the optical recording medium and the flat surfaceportion of the solid immersion lens, comprising a beam splitter forreflecting both of a p-polarized light component and an s-polarizedlight component in reflected light beams from the optical recordingmedium, a dividing device for dividing the p-polarized light componentand the s-polarized light component reflected by the beam splitter and aphoto-detecting device for separately detecting the p-polarized lightcomponent and the s-polarized light component divided by the dividingdevice.

According to another aspect of the present invention, there is provideda recording and reproducing apparatus for recording and/or reproducingan optical recording medium by using an optical pickup device includinga condenser lens composed of a solid immersion lens having a sphericalsurface portion and a flat surface portion parallel to the surface ofthe optical recording medium, the condenser lens having a numericalaperture greater than 1, the optical pickup device comprising a beamsplitter for reflecting both of a p-polarized light component and ans-polarized light component in reflected light beams from the opticalrecording medium, a dividing device for dividing the p-polarized lightcomponent and the s-polarized light component reflected by the beamsplitter and a photo-detecting device for separately detecting thep-polarized light component and the s-polarized light component dividedby the dividing device, comprising a drive device for adjusting adistance between the optical recording medium and the flat surfaceportion of the solid immersion lens and a control device for controllingthe adjustment state of the drive device based upon a detected signalobtained when light intensity of one polarized component detected by thephoto-detecting means is detected as a signal corresponding to thedistance between the surface of the optical recording medium and theflat surface portion of the solid immersion lens.

In accordance with a further aspect of the present invention, there isprovided a gap detection method for detecting a gap between a flatsurface portion of a solid immersion lens and an optical recordingmedium by an optical pickup device including a condenser lens composedof the solid immersion lens having a spherical surface portion and aflat surface portion parallel to the surface of the optical recordingmedium, the condenser lens having a numerical aperture greater than 1when a bundle of rays in a predetermined polarized state is irradiatedon the optical recording medium from a light source, comprising thesteps of irradiating the optical recording medium with a bundle of raysin a predetermined polarized state through the condenser lens,reflecting both of a p-polarized light component and an s-polarizedlight component of reflected light of the light beam after the lightbeam has irradiated the recording medium, dividing the thus reflectedp-polarized light component and s-polarized light component and deviceaccording to a second embodiment of the present invention, wherein FIG.16A is a side view of the optical pickup device and FIG. 16B is a planview showing a pattern of a photo-detector for use with the opticalpickup device shown in FIG. 16A;

FIGS. 17A and 17B are respectively diagrams to which reference will bemade in explaining a Glan-Thompson prism which is applicable to theoptical pickup device according to the second embodiment of the presentinvention, wherein FIG. 17A is a diagram showing an arrangement of theGlan-Thompson prism and FIG. 17B is a diagram showing polarizationdirections of respective prisms;

FIGS. 18A and 18B are respectively diagrams showing an arrangement of anexample of a main portion of an optical pickup device according to athird embodiment of the present invention, wherein FIG. 18A is a sideview of the optical pickup device and FIG. 18B is a plan view showing apattern of a photo-detector for use with the optical pickup device shownin FIG. 18A;

FIGS. 19A, 19B and 19C are respectively diagrams to which reference willbe made in explaining a polarizing and dividing grating which isapplicable to the optical pickup device according to the thirdembodiment of the present invention, wherein FIG. 19A is a perspectiveview showing an arrangement of the polarizing and dividing grating, FIG.19B is a diagram showing the polarization directions in the polarizingand dividing grating and FIG. 19C is a diagram showing an arrangement ofthe polarizing and dividing grating in cross-section; and

FIG. 20 is a block diagram showing an example of an detecting a distancebetween the optical recording medium and the flat surface portion of thesolid immersion lens based upon light intensity of any one polarizedlight component of the thus divided p-polarized light component ands-polarized light component.

According to the present invention, since a beam splitter is provided toreflect both of a p-polarized light component and a s-polarized lightcomponent, the p-polarized light component and the s-polarized lightcomponent thus reflected by the beam splitter are divided and lightintensity of one of the thus divided polarized light components isdetected, it becomes possible to detect a signal corresponding to adistance between a flat surface portion of a solid immersion lens andthe surface of an optical recording medium by a simple and efficientarrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing an example of an arrangement of an opticalpickup device according to the related art;

FIGS. 2A and 2B are respectively explanatory diagrams showing Xcomponent and Y component of an electric field of a bundle of raysincident on an optical recording medium in the optical pickup device ofthe example of the related art shown in FIG. 1;

FIGS. 3A and 3B are respectively longitudinal cross-sectional viewsshowing the state in which a solid immersion lens in the optical pickupdevice is in close contact with the optical recording medium;

FIGS. 4A and 4B are respectively explanatory diagrams showingdistributions of returned light returned from the optical recordingmedium when the solid immersion lens in the optical pickup device is inclose contact with the optical recording medium;

FIG. 5 is a longitudinal cross-sectional view showing the state in whichthe solid immersion lens in the optical pickup device is distant fromthe optical recording medium;

FIGS. 6A and 6B are respectively explanatory diagrams showingdistributions of returned light returned from the optical recordingmedium when the solid immersion lens in the optical pickup device isdistant from the optical recording medium;

FIG. 7 is a diagram showing characteristic curves to which referencewill be made in explaining an example of a relationship between adistance between the solid immersion lens in the optical pickup deviceand the optical recording medium and a gap error signal;

FIG. 8 is a side view showing other example of an arrangement of anoptical pickup device according to the related art;

FIG. 9 is a side view showing a further example of an arrangement of anoptical pickup device according to the related art;

FIG. 10 is a longitudinal cross-sectional view showing the state inwhich a solid immersion lens in the optical pickup device in the exampleshown in FIG. 9 is in close contact with the optical recording medium;

FIGS. 11A and 11B are respectively explanatory diagrams showingdistributions of light beams returned from the optical recording mediumwhen the solid immersion lens in the optical pickup device in theexample shown in FIG. 9 is in close contact with the optical recordingmedium;

FIGS. 12A and 12B are respectively explanatory diagrams showingdistributions of light beams returned from the optical recording mediumwhen the solid immersion lens in the optical pickup device in theexample shown in FIG. 9 is distant from the optical recording medium;

FIG. 13 is a diagram showing characteristic curves to which referencewill be made in explaining a relationship between the distance betweenthe solid immersion lens in the optical pickup device in the exampleshown in FIG. 9 and the optical recording medium and a gap error signal;

FIGS. 14A and 14B are respectively diagrams showing an arrangement of anexample of a main portion of an optical pickup device according to afirst embodiment of the present invention, wherein FIG. 14A is a sideview of the optical pickup device and FIG. 14B is a plan view of apattern of a photo-detector for use with the optical pickup device shownin FIG. 14A;

FIGS. 15A and 15B are respectively diagrams to which reference will bemade in explaining a Wollaston prism that is applicable to the opticalpickup device according to the first embodiment of the presentinvention, wherein FIG. 15A is a diagram showing an arrangement of theWollaston prism and FIG. 15B is a diagram showing polarizationdirections in the respective prisms;

FIGS. 16A and 16B are respectively diagrams showing an example of a mainportion of an arrangement of an optical pickup arrangement of a servosystem that is applicable to the first, second and third embodiments ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described below.

Prior to the detailed description of the arrangement of the presentinvention, definitions of terms that will be used in the followingdescriptions will be described below in order to understand the presentinvention more clearly. In this specification, the term “opticalrecording and reproducing apparatus” refers to not only a “recording andreproducing apparatus for recording and reproducing an optical recordingmedium” but also a “recording apparatus for recording an opticalrecording medium” and a “reproducing apparatus for reproducing anoptical recording medium”. Moreover, as has already been described, theterm “optical recording medium” also refers to other recording mediumssuch as a “magneto-optical recording medium in and from whichinformation can be recorded and reproduced optically”.

A first embodiment of the present invention will be described withreference to FIGS. 14A, 14B and FIGS. 15A, 15B.

FIGS. 14A and 14B are diagrams showing an arrangement of an opticalpickup device according to a first embodiment of the present invention.As shown in FIGS. 14A and 14B, this optical pickup device includes asemiconductor laser 101 prepared as a light source, and a bundle of raysfrom this semiconductor laser 101 is introduced into a beam splitter102. A bundle of rays emitted from the semiconductor laser 101 istransmitted through the beam splitter 102 and introduced into aquarter-wave plate (λ/4 plate) 103. The quarter-wave plate 103 isdisposed such that its crystallographic axis is inclined at aninclination angle of 45° relative to the direction of polarization ofincident light. The light that has become incident on the quarter-waveplate 103 is double-refracted as circularly polarized light and thiscircularly polarized light is introduced through a condenser lenscomposed of an objective lens 104 and a solid immersion lens (SIL) 105into the signal recording surface of the optical recording medium 90.

As has been so far described as the related-art technology, the solidimmersion lens 105 is disposed very close to the surface of the opticalrecording medium 90 (e.g. distance of about 50 nm) and is of a so-calledhemispherical lens in which one surface on the side close to the opticalrecording medium 90 is shaped as a flat surface, the other surface closeto the objective lens 104 is shaped as a spherical surface, a thicknessthereof being selected to be the same as the radius of the sphericalsurface. Alternatively, the solid immersion lens 105 may be shaped likea super-hemispherical type lens having a thickness larger than theradius of the spherical surface comprising the lens. Moreover, withrespect to the surface of the side close to the optical recording medium90, only the central portion through which a bundle of rays of laserlight is transmitted may be formed as a flat surface and the marginalportion around the central portion may be formed as a suitable shapesuch as a cone. In the following description, the surface of the sideclose to the optical recording medium 90 will be simply referred to as a“flat surface”. Herein, a “flat surface” refers to a flat surface inwhich a surface portion through which at least a bundle of rays of laserlight is transmitted may be formed as a flat surface, and the whole ofthis surface portion need not always be shaped as the flat surface.

In this manner, since the objective lens 104 and the solid immersionlens 105 constitute the condenser lens, the numerical aperture (NA) ofthe condenser lens becomes greater than 1, and hence it becomes possibleto record and reproduce information by the near-field optical recordingand reproducing system.

Light that has been reflected on the surface of the optical recordingmedium 90 is introduced through the solid immersion lens 105 and theobjective lens 104 into the quarter-wave plate 103. Light introducedinto the quarter-wave 103 is double-refracted and thereby changed fromcircularly polarized light into linearly polarized light. The, the lightthat has transmitted through the quarter-wave plate 103 is introducedinto the beam splitter 102. This beam splitter 102 is not a polarizationbeam splitter but may be a beam splitter for polarizing a bundle of raysintroduced thereinto from the side of the optical recording medium 90 toprovide two polarized light components of an s-polarized light componentand a p-polarized light component so that the two polarized lightcomponents may be reflected to the lateral direction. Specifically, inthis beam splitter 102, its reflected light is given the same polarizedlight component as that of the light from the light source, and the beamsplitter 102 reflects 50% of the light incident thereon from theobjective lens 104, for example, to the lateral direction by thereflection surface thereof.

The returned light that has been reflected to the lateral direction bythe beam splitter 102 is introduced into a dividing means for dividingincident light into an s-polarized light component and a p-polarizedlight component. In this embodiment, a Wollaston prism 110 is used asthe dividing means. The incident light is divided into an s-polarizedlight component and a p-polarized light component by the Wollaston prism110, and the thus divided s-polarized light component and p-polarizedlight component are introduced into an RF (radio frequency) signaldetecting unit 121 and a gap error signal detecting unit 122 which areadjoining to each other on the same plane of the photo-detector 120.

As shown in FIGS. 15A and 15B, the Wollaston prism 110 is composed of afirst prism 111 and a second prism 112 that are joined to each other insuch a manner that C axes of crystals of two prisms thereof may becomedifferent from each other 90°. When incident light is refracted on ajoint surface 113 of the two prisms 111 and 112, polarized light in thesame direction as the C-axis direction of the first prism 111 is givenan emission angle θ₀ (incidence angleθ₁) that can satisfy n₁ sin θ₁=n₂sin θ₀ on the joint surface 113. Moreover, polarized light in theopposite direction of the C-axis direction of the first prism 111 isgiven the emission angle θ₀ that can satisfy n₂ sin θ₁=n₁ sin θ₀ on thejoint surface 113.

Accordingly, the photo-detector 120 having the two adjacentphoto-detecting units 121, 122 on the same plane is disposed at a lightemission portion from which the light that has transmitted through thisWollaston prism 110 is emitted, whereby the s-polarized light componentis introduced into the RF signal detecting unit 121 of thephoto-detector 120 and the p-polarized light component is introducedinto the gap error signal detecting unit 122 of the photo-detector 120.The signal introduced into the RF signal detecting unit 121 becomes asignal corresponding to concavities and convexities of the pits of theoptical recording medium 90 so that information can be reproduced fromthe optical recording medium 90. The signal introduced into the gaperror signal detecting unit 122 becomes a gap error signal of which thelight intensity changes in response to the distance (air gap) betweenthe surface of the optical recording medium 90 and the flat surfaceportion of the solid immersion lens 105.

The p-polarized light component becomes the gap error signal based uponthe same principle as that which has already been referred to as therelated-art technology. Specifically, by detecting a component of thepolarized state perpendicular to the polarized state of reflected lightobtained when the distance between the surface of the optical recordingmedium 90 and the flat surface portion of the solid immersion lens 105is zero from the reflected light (returned light) that was reflected bythe optical recording medium 90 after they have been emitted from thesemiconductor laser 101, it is possible to obtain the gap error signalcorresponding to the distance between the surface of the opticalrecording medium 90 and the flat surface portion of the solid immersionlens 105.

By using the thus detected gap error signal, it becomes possible toservo-control the distance between the optical recording medium 90 andthe solid immersion lens 105. A servo control mechanism will bedescribed later on.

With the arrangement shown in FIGS. 14A, 14B and FIGS. 15A, 15B, thes-polarized light component and the p-polarized light component of thereflected light from the optical recording medium 90 can separately bedetected by the simple arrangement using one beam splitter 102 and theWollaston prism 110 serving as the dividing means for dividing incidentlight into the s-polarized light component and the p-polarized lightcomponent, the optical pickup device can be simplified in arrangement ascompared with the related-art optical pickup device using a plurality ofbeam splitters, and hence the optical pickup device can be miniaturizedin size. Moreover, with respect to the photo-detector, it is sufficientto prepare one photo-detector 120 that can detect the two polarizedlight components emitted from the Wollaston prism 110 at the adjacenttwo photo-detection positions on the same plane, and hence thephoto-detector can be simplified in arrangement as compared with thecase in which a plurality of photo-detectors are separately located atthe different positions like the related-art. When the optical pickupdevice according to this embodiment is attached to the optical recordingand reproducing apparatus, the recording and reproducing apparatus canbe simplified in arrangement and miniaturized in size.

A second embodiment of the present invention will be described withreference to FIGS. 16A, 16B and FIGS. 17A, 17B. In FIGS. 16A, 16B andFIGS. 17A, 17B, elements and parts identical to those of FIGS. 14A, 14Bthat have been referred to in the first embodiment are denoted by theidentical reference numerals.

According to this embodiment, while the Wollaston prism is used as thedividing means for dividing the incident light into the p-polarizedlight component and the s-polarized light component in the firstembodiment, this embodiment uses a Glan-Thompson lens as the dividingmeans. A rest of the arrangement of the optical system is the same asthat of the optical pickup device that has been described in the firstembodiment.

Specifically, as shown in FIGS. 16A, 16B, there is prepared thesemiconductor laser 101 as the light source, and a bundle of rays fromthis semiconductor laser 101 is introduced into the beam splitter 102. Abundle of rays incident on the beam splitter 102 from the semiconductorlaser 101 is traveled through the beam splitter 102 and introduced intothe quarter-wave plate (λ/4 plate) 103. The quarter-wave plate 103 isdisposed such that its crystallographic axis is inclined at aninclination angle of 45° relative to the direction of polarization ofthe incident light. The quarter-wave plate 103 double-refracts theincident light to provide circularly polarized light. The circularlypolarized light from the quarter-wave plate 103 is introduced into thesignal recording surface of the optical recording medium 90 through acondenser lens composed of the objective lens 104 and the solidimmersion lens (SIL) 105, the condenser lens having the numericalaperture (NA) greater than 1.

Light that has been reflected on the surface of the optical recordingmedium 90 is introduced through the solid immersion lens 105 and theobjective lens 104 into the quarter-wave plate 103. The quarter-waveplate 103 double-refracts the incident light to change circularlypolarized light to linearly polarized light. A bundle of rays that hastransmitted through the quarter-wave plate 103 is introduced into thebeam splitter 102. The beam splitter 102 is not the polarization beamsplitter but may be a beam splitter for reflecting both of polarizedlight components of an s-polarized light component and a p-polarizedlight component of a bundle of rays introduced thereinto from the sideof the optical recording medium 90 to the lateral side.

The returned light reflected to the lateral side by the beam splitter102 is introduced into the dividing means that divides incident lightinto an s-polarized light component and a p-polarized light component.In this embodiment, a Glan-Thompson prism 130 is used as the dividingmeans. The incident light is divided into an s-polarized light componentand a p-polarized light component by the Glan-Thompson prism 130, andthe thus divided s-polarized light component and p-polarized lightcomponent are introduced into an RF (radio frequency) signal detectingunit 141 and a gap error signal detecting unit 142 which are adjacent toeach other on the same plane of a photo-detector 140.

The Glan-Thompson prism 130 comprises a glass 131 and a prism 132 whichare joined together on a joint surface 133 as shown in FIGS. 17A. 17B.When incident light is refracted on the joint surface 133 of theGlan-Thompson prism 130, polarized light polarized in the same directionas the C-axis direction of the prism 132 is given an emission angle θ₀(incidence angleθ₁) that can satisfy n_(G) sin θ₁=n₁ sin θ₀ on the jointsurface 133. Moreover, polarized light polarized in the oppositedirection of the C-axis direction of the prism 132 is given an emissionangle θ₀ that can satisfy n_(G) sin θ₁=n₂ sin θ₀ on the joint surface133.

Accordingly, the photo-detector 140 having the adjacent twophoto-detecting units 141, 142 on the same plane is located at a lightemission portion from which light that has transmitted through theGlan-Thompson prism 130 is emitted, whereby the s-polarized lightcomponent is introduced into the RF signal detecting unit 141 of thephoto-detector 140 and the p-polarized light component is introducedinto the gap error signal detecting unit 142 of the photo-detector 140.Since the Wollaston prism 110 that has been described in the firstembodiment and the Glan-Thompson prism 130 have different emissionangles of two polarized light components, the photo-detector 140 used inthis embodiment has to locate its respective photo-detecting units 141,142 at slightly different positions from those at which thephoto-detector 120 that has been described in the first embodiment haslocated its respective photo-detecting units 121 and 122.

With this arrangement, the signal that is introduced into the RF signaldetecting unit 141 becomes a signal corresponding to concavities andconvexities of the pits on the optical recording medium 90 so thatinformation can be reproduced from the optical recording medium 90. Thesignal that is introduced into the gap error signal detecting unit 142becomes a gap error signal of which the light intensity changes inresponse to the distance between the surface of the optical recordingmedium 90 and the flat surface portion of the solid immersion lens 105.By using this gap error signal, it becomes possible to servo-control thedistance between the optical recording medium 90 and the solid immersionlens 105. Accordingly, similarly to the optical pickup device that hasbeen described so far in the first embodiment, also in this embodiment,the optical pickup device can be simplified in arrangement andminiaturized in size, by which the recording and reproducing apparatuscan be simplified in arrangement and miniaturized in size.

A third embodiment of the present invention will be described withreference to FIGS. 18A, 18B and FIGS. 19A, 19B, 19C. In FIGS. 18A, 18Band FIGS. 19A, 19B, 19C, elements and parts identical to those of FIGS.14A, 14B and FIGS. 16A, 16B that have been described in the first andsecond embodiments are denoted by the identical reference numerals.

According to this embodiment, while the Wollaston prism or theGlan-Thompson prism was used as the dividing means for dividing incidentlight into the p-polarized light component and the s-polarized lightcomponent in the first and second embodiments, according to thisembodiment, a polarizing and dividing grating is used as the dividingmeans. A rest of fundamental arrangement of the optical system is thesame as that of the arrangements of the optical pickup devices that havebeen described so far in the first and second embodiments.

Specifically, as shown in FIGS. 18A, 18B, the semiconductor laser 101 isprepared as the light source, and a bundle of rays from thissemiconductor laser 101 is introduced into the beam splitter 102. Abundle of rays incident on the beam splitter 102 from the semiconductorlaser 101 transmits through the beam splitter 102 and becomes incidenton the quarter-wave plate (λ/4 plate) 103. The quarter-wave plate 103 isdisposed such that its crystallographic axis is inclined at aninclination angle of 45° relative to the direction of polarization ofincident light. The quarter-wave plate 103 double-refracts the incidentlight to provide circularly polarized light, and the circularlypolarized light from the quarter-wave plate 103 is introduced into thesignal recording surface of the optical recording medium 90 through thecondenser lens composed of the objective lens 104 and the solidimmersion lens (SIL) 105, the condenser lens having a numerical aperture(NA) greater than 1.

Light reflected on the surface of the optical recording medium 90 isintroduced into the quarter-wave plate 103 through the solid immersionlens 105 and the objective lens 104. The quarter-wave plate 103double-refracts the circularly polarized light to provide linearlypolarized light. A bundle of rays that has passed through thequarter-wave plate 103 is introduced into the beam splitter 102. Thebeam splitter 102 is not a polarization beam splitter but is a beamsplitter for reflecting a bundle of rays incident thereon from the sideof the optical recording medium 90 as two polarized light components ofan s-polarized light component and a p-polarized light component to thelateral direction.

The returned light that has been reflected toward the lateral side bythe beam splitter 102 is introduced into a dividing means for dividingincident light into an s-polarized light component and a p-polarizedlight component. In this embodiment, a polarizing and dividing grating150 is used as the dividing means. The incident light is divided into ans-polarized light component and a p-polarized light component by thepolarizing and dividing grating 150, and the thus divided s-polarizedlight component and p-polarized light component are introduced intoadjacent three photo-detecting units 161, 162, 163 on the same plane ofa photo-detector 160. The p-polarized light component is divided intotwo p-polarized light components and the thus divided two p-polarizedlight components are introduced into the two photo-detecting units 161and 163. The s-polarized light component is introduced into thephoto-detecting unit 162.

The polarizing and dividing grating 150 has a substrate made of crystalsuch as LiNbO₃ in which a hydrogen substitution region 151 with lithium(Li) substituted with hydrogen (H) is formed on the surface of thesubstrate like a grating, a refractive index of the hydrogensubstitution region 151 being selected to be n₂ regardless of thedirection of polarization. Assuming now that the thickness of thehydrogen substitution region 151 is T, then with respect to thepolarized light component of the C-axis direction, a phase difference of2π(n₁−n₂)T/λ occurs between the hydrogen substitution region 151 andother region and thereby the polarizing and dividing grating 150 acts asa grating. On the other hand, with respect to the polarized lightcomponent of the direction opposite to the C-axis direction, arefractive index difference does not occur between the hydrogensubstitution region 151 and other region, and hence incident lighttransmits through the polarizing and dividing grating 150 without beingdiffracted. Assuming that P is the pitch of the grating, then an angle θof the polarized component of the diffracted C-axis direction is givenby λ/P=sin θ.

Accordingly, the photo-detector 160 with the adjacent threephoto-detecting units 161, 162, 163 on the same plane is located at alight emission portion from which light that has passed through thispolarizing and dividing grating 150 is emitted, whereby the p-polarizedlight component is introduced into the two gap error signal detectingunits 161 and 163 and a gap error signal is obtained by using any one ofthe signals obtained at the two gap error signal detecting units 161,163 or by using a signal which results from adding the two signalsobtained from the two gap error signal detecting units 161, 163. Thisgap error signal has light intensity that changes in response to thedistance between the surface of the optical recording medium 90 and theflat surface portion of the solid immersion lens 105. By using this gaperror signal, it becomes possible to servo-control the distance betweenthe optical recording medium 90 and the solid immersion lens 105 becomespossible.

The s-polarized light component is introduced into the RF signaldetecting unit 162 and the signal outputted from this RF signaldetecting unit 162 becomes the signal corresponding to concavities andconvexities of the pits on the optical recording medium 90 so thatinformation can be reproduced from the optical recording medium 90.Accordingly, similarly to the optical pickup devices that have beendescribed in the first and second embodiments, also in this embodiment,the optical pickup device can be simplified in arrangement andminiaturized in size, by which the recording and reproducing apparatuscan be simplified in arrangement and miniaturized in size.

A servo mechanism for servo-controlling the position of the opticalsystem when the optical recording and reproducing medium is recorded orreproduced with application of the optical pickup devices of theabove-mentioned respective embodiments will be described with referenceto FIG. 20. When the optical recording medium such as an optical diskand a magneto-optical disk is recorded or reproduced by using theoptical pickup device, the positions of suitable assemblies such as alens should be servo-controlled by using a servo mechanism.Particularly, this example requires a servo mechanism by which adistance between the surface of the optical recording medium 90 and theflat surface portion of the solid immersion lens 105 can be held at apredetermined distance. As shown in FIG. 20, this servo mechanismincludes a coil 20 serving as a means for moving the solid immersionlens 105 in the direction perpendicular to the surface of the opticalrecording medium 90, a servo circuit 21 and a control circuit 22 servingas a control means for controlling this servo circuit 21. The servocircuit 21 is able to set the distance between the surface of theoptical recording medium 90 and the flat surface portion of the solidimmersion lens 105 to the state instructed by the control circuit 22 inresponse to a signal applied to the coil 20.

The control circuit 22 supplies a command to the servo circuit 21 so asto maintain the light intensity of the gap error signal, detected by thegap error signal detecting unit 122 of the photo-detector 120 (in thecase of the first embodiment), at predetermined light intensity, therebymaintaining a constant distance between the surface of the opticalrecording medium 90 and the flat surface portion of the solid immersionlens 105. Herein, the solid immersion lens 105 can be controlled inposition in unison with the objective lens 104 by the coil 20.

To maintain the light intensity detected by the photo-detector 122 atpredetermined intensity, the output signal from the photo-detector 122,for example, is compared with a predetermined reference value. Thisreference value can be determined by the following first, second andthird processing, for example.

The first processing is such one that a mean value between an outputvalue outputted from the gap error signal detecting unit 122 when thesurface of the optical recording medium 90 and the flat surface portionof the solid immersion lens 105 are in close contact with each other(distance therebetween is zero) and an outputted value outputted fromthe gap error signal detecting unit 122 when a distance between thesurface of the optical recording medium 90 and the flat surface portionof the solid immersion lens 105 is sufficiently large is set to areference value. In the second processing, a distance between thesurface of the optical recording medium 90 and the flat surface portionof the solid immersion lens 105 is measured, correlation between thismeasured value and the outputted value from the gap error signaldetecting unit 122 is calculated, whereafter an outputted valuecorresponding to a predetermined distance is specified and set to areference value. Further, the third processing is such one that ½ of thevalue outputted from the gap error signal detecting unit 122 when thedistance between the surface of the optical recording medium 90 and theflat surface portion of the solid immersion lens 105 is sufficientlylarge is set to a reference value. Any one of the first, second andthird processing may be applied to the present invention.

As shown in FIG. 20, the output from the RF signal detecting unit(detecting unit 121 in the first embodiment) of the photo-detector(photo-detector 120 in the first embodiment) is supplied to areproducing block 24, in which it is processed by reproducing processingto thereby making it possible to reproduce information from the opticalrecording medium 90. When information is recorded on the opticalrecording medium 90, record processing can be carried out by generatinga drive signal for driving the semiconductor laser 101 (in the case ofthe recording medium in which information is recorded by using pits orphase-change) or a drive signal for driving a magnetic field modulationcoil (in the case of a magneto-optical recording medium) based upon asignal that has been processed by a recording block 25. The servocircuit 21 is not limited to the above-mentioned servo-control operationfor servo-controlling the distance between the surface of the opticalrecording medium 90 and the flat surface portion of the solid immersionlens 105 and it may servo-control a spindle motor 26 that rotates theoptical recording medium 90.

The present invention is not limited to the above-mentioned embodimentsand may take various arrangements without departing from the gist of thepresent invention. By way of example, as the dividing means for dividingthe incident light into the p-polarized light wave and the s-polarizedlight wave, there can be used other dividing means than the Wollastonprism, the Glan-Thompson prism and the polarizing and dividing gratingin the above-mentioned first, second and third embodiments. Even whenthe polarizing and dividing grating is in use, there can be used apolarizing and dividing grating composed of other crystal structure thanthe crystal structure that has been referred to in the above-mentionedembodiments. Furthermore, the servo mechanism is not limited to theabove-mentioned servo mechanism having the arrangement shown in FIG. 20and may be modified as a servo mechanism for driving a suitablecomponent such as a solid immersion lens.

According to the present invention, since the beam splitter reflectsboth of the p-polarized light component and the s-polarized lightcomponent, the p-polarized light component and the s-polarized lightcomponent reflected by this beam splitter are divided from each otherand the light intensity of one of the divided polarized light componentis detected, it becomes possible to detect the distance between the flatsurface portion of the solid immersion lens and the surface of theoptical recording medium by the simple and efficient arrangement.

In this case, since the Wollaston prism, the Glan-Thompson prism or thepolarizing and dividing grating is used as the dividing means, forexample, the p-polarized light component and the s-polarized lightcomponent can be divided from each other by the simple arrangement, andhence it becomes possible to individually detect the p-polarized lightcomponent and the s-polarized light component.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

1. An optical pickup device including a condenser lens composed of asolid immersion lens having a spherical surface portion and a flatsurface portion parallel to the surface of an optical recording medium,said condenser lens having a numerical aperture greater than 1, a bundleof rays in a predetermined polarized state being irradiated on saidoptical recording medium from a light source through said condenser lensand a polarized state component perpendicular to the polarized state ofreflected light obtained when a distance between the surface of saidoptical recording medium and the flat surface portion of said solidimmersion lens is zero is detected from reflected light from saidoptical recording medium to obtain a signal corresponding to thedistance between the surface of said optical recording medium and theflat surface portion of said solid immersion lens, comprising: a beamsplitter configured to reflect both of a p-polarized light component andan s-polarized light component in reflected lights from said opticalrecording medium; a divider configured to divide incident light into thep-polarized light component and the s-polarized light componentreflected by said beam splitter; and a photo-detector configured toseparately detect the p-polarized light component and the s-polarizedlight component separated by said divider.
 2. An optical pickup deviceaccording to claim 1, wherein said divider is a Wollaston prism.
 3. Anoptical pickup device according to claim 1, wherein said divider is aGlan-Thompson prism.
 4. An optical pickup device according to claim 1,wherein said divider is a polarizing and dividing grating.
 5. Arecording and reproducing apparatus for recording and/or reproducing anoptical recording medium by using an optical pickup device including acondenser lens composed of a solid immersion lens having a sphericalsurface portion and a flat surface portion parallel to the surface ofsaid optical recording medium, the condenser lens having a numericalaperture greater than 1, said optical pickup device comprising a beamsplitter configured to reflect both of a p-polarized light component andan s-polarized light component in reflected lights from said opticalrecording medium, a divider configured to divide the p-polarized lightcomponent and the s-polarized light component reflected by said beamsplitter, and a photo-detector configured to separately detect thep-polarized light component and the s-polarized light component dividedby said divider, comprising: a drive unit configured to adjust adistance between said optical recording medium and said flat surfaceportion of said solid immersion lens; and a controller configured tocontrol the adjustment state of said drive unit based upon a detectedsignal obtained when light intensity of one polarized component detectedby said photo-detector is detected as a signal corresponding to thedistance between the surface of said optical recording medium and theflat surface portion of said solid immersion lens.
 6. A recording andreproducing apparatus according to claim 5, further comprising: areproducer configured to reproduce information from said opticalrecording medium based upon the other polarized light component detectedby said photo-detector.